Fuel metering devices for ram jet engines



Nov. 11, 1958 v D. w. GUNNARS-ON 2,859,589

FUEL METERING DEVICES FOR RAM JET ENGINES Filed June 20, 1950 /0 /6 /z A A A IN VEN TOR.

DAN/EL PV- GUNNAESON United States Patent FUEL METERING DEVICES FOR RAM JET ENGINES Daniel W. Gunnarson, Seattle, Wash, assignor to Boeing Airplane Company, Seattle, Wasln, a corporation of Delaware Application June 20, 1951), Serial No. 169,144 1 Claim. c1. 60 39.28)

This invention relates to apparatus for automatically regulating the rate at which fuel is supplied to a ram jet engine operating within a given supersonic air speed range, the purpose being to maintain substantially constant the ratio between quantity of fuel supplied and quantity of air entering the engine. A primary application of the invention is, of course, in supersonic speed aircraft. The main object of the invention is to achieve such regulation by apparatus which is simple, compact, light-weight, and employs a minimum of moving parts.

The present invention has its beginnings in my discovery of the fact that the pressure developed in a pitot tube having its mouth located outside a ram jet engine and away from its shock waves varies with air speed, over a substantial supersonic range, in approximately direct proportion to the variation in the quantity of air entering the engine by ram effect. It is found, therefore, that such pressure may be used as the basis of direct control over the flow of fuel to the engines burners for constantly maintaining the fuel-to-air ratio mentioned above.

An interesting and unusual aspect of this discovery is that the accuracy of this relationship between pitot pres sure and air speed, affording a basis of such regulation, is improved by the presence of the small shock wave in front of the pitot tubes month, by which it is caused, and that purely free-stream total pressure, as such, is

less accurately proportional to the quantity of air flowing into the engine during variations in air speed. I

As will be explained later herein the supersonic speed range over which this basis of fuel supply regulation is applicable is determined by certain outward physical or aerodynamic design features of the ram jet engine structure. For a given design, the regulatory range can be ascertained readily by wind tunnel Schlieren tests, for example.

In the preferred and illustrated apparatus for applying this discovery in a practical case, the pitot pressure is applied to an evacuated bellows which, against the force of a control spring, moves a valve in the fuel delivery line to the jet burners to provide a restriction to flow which increases or decreases as pitot pressure decreases or increases, respectively. Between this valve and the engine is located a second variable flow-restricting valve actuated in accordance with variations in the differential of pressure in the fuel line as between opposite sides of the first valve. This second valve removes the effect of fuel pressure variations as an influence on rate of flow of fuel to the engine.

These and other features, objects and advantages of the invention, including certain details of the preferred form of mechanism for practicing the same will now be described in greater detail by reference to the accompanying drawings.

Figure 1 is a side elevational view, with parts broken away, of the forward end of a typical ram jet engine structure. I

Figure 2 is a sectional view, partly diagrammatic, of a 2,859,589 Patented Nov. 11, 1958 preferred form of fuel-regulating apparatus arranged to operate according to the invention.

In the usual ram jet engine as shown in Figure 1, there is a generally cylindrical cowl or outer shell 10, the forward end portion of which is slightly tapered forwardly'and terminates in a circular rim or lip 12 which splits the airstream into a portion entering the engine and a portion flowing past it, and is sometimes referred to as the diffuser. The shape of the rear portion of this outer shell is not material as far as the present invention is concerned and may be considered to be conventional, only the forward portion of the engine being shown in the figure. The generally torpedo-shaped island 14 is mounted coaxially within the outer shell by radial struts 16. This island contains various parts of the engine, including fuel supply and regulating apparatus. The forward end portion of the island, which terminates in a generally conically tip 18, projects appreciably ahead of the diffuser lip 12 as shown, the particular tip being ogival.

In the illustrated case, the pitot tube 20, utilized in conjunction with fuel supply regulating apparatus, resembles a spike projecting forwardly from the ogival tip 18 along the longitudinal axis of the engine structure. The projecting length of the pitot tube is more or less immaterial as long as its mouth is disposed out of the region of any major shock waves such as those which originate by impact of the islands conical tip 18 on the airstream. Beyond the requirement that the pitot tube create negligible drag, its outside diameter is not important, a diameter of one-quarter of an inch being satisfactory. Nor is the diameter of the bore in this tube critical since there is no actual airflow through it, a diameter of one-sixteenth of an inch being satisfactory.

When the speed of the aircraft increases through the transition from sonic into the supersonic'range, above Mach No. 1, a shock wave A1 is set up ahead of the engines forwardmost point, the islands conical tip 18, designated a bow wave. As speed is further increased, a speed is reached at which this bow wave shifts rearward quite suddenly and assumes a generally conical shape hugging the conical tip 18, as indicated at A2. The supersonic speed at which this shift occurs will depend upon the shape of the engine structure, and more particularly upon the cone angle of the conical tip 18. In the illustrated case wherein the cone tip angle is about 50 degrees, the shock wave shifts to the cone tip, generally in the position A2, at a speed of about Mach No. 1.33. It does so at a lower speed for a smaller cone angle and at a higher speed for a larger cone angle. The speed at which this shift takes place represents the lower limit of the range in which pitot pressure control over fuel supply rate is applicable in accordance with this invention.

As speed further increases the location of the apex of the shock wave does not materially change, but its sweepback or cone angle decreases. Such angle continues to decrease until, at the upper limit of the speed range of interest, the wave encounters interference from the diffuser lip 12, which in the example occurs at a speed just slightly under Mach No. 2. The waves position at this speed is indicated by the designation A3 in Figure l.

A pitot tube 20 projecting directly forwardly from conical tip 18 of island 14 develops an internal pressure which, within the speed range in which the main shock wave lies between the position A2 and the position A3, is an approximately accurate measure of quantity of air entering the cowl 10 by ram effect. The accuracy of this itself creates ahead of it, and which exists over the entire speed range between the above-described limits. The

relationship varies slightly-with speed and with altitude but is still a more accurate measure of fuel-requirements for a constant fuel-to-air ratio than that produced by more complex arrangements known heretofore. The

lines B2 and B3 are intended-to represent the positionsofthe pitot tube shock wave atspeedscorresponding respec-= tively to .those at whichthe wave positions A2 and A3 exist.

discovery,

22 tothe pressure chamber 24 tends directly to contractthe evacuated bellows 26,: a n action opposed-by a spring; 28 which,:through a control rod '30 threadedly connected to the-inner end of the bellows as shown, tends to stretch out the-bellows againstthe effect of pitot pressure-.-- The opposite or outer end of thebellows is securely anchoredby a screw 32 to the outer end wall of the housing--24.

The'open innerendof housing 24 is bolted to one endof the casing 42 of a control valve 34, with the-cover plate or gasket 42a sandwiched therebetween. The-control rod passesrslidably through a central aperture in thisgasket, in which it is sealed against leakageof fuel past such rod. The control rod has sufiicient length to extend from the evacuated bellows 26 through the valve housing 42. and through-and beyond the opposite cover plate 42b on the opposite side of the valve housing. The control rod passes slidably through an aperture in cover plate 42b and is sealed-therein against leakage of fuel from inside the valve casing past the rod. The rods projecting end is threaded and receives a nut serving as an adjustable stop for the collar 38. The Spring 28 encircling the control rod 30 outside the valve casing is compressed between the collar 38 and the base of a groove in the exterior face of the cover plate 42b.

The valve casing 42 has a central generally cylindrical chamber 42c concentric with control rod 30. A valve insert sleeve 44 fits snugly within this chamber, clamped between the end plates 42a and 42b. The valve casing alsohas a fuel passage or bore 36 extending transversely through it and generally intersecting the chamber 420 at-- right angles. The ends of connecting segments of fuel; line.48 fit into the respectively opposite ends of the bore 36. Fuel enters the valve casing 42 through the segment of fuel line 48.at the left in Figure 2, connected to and comprising part of the fuel supply means (not shown),

and'leaves the valve casing through the fuel line segment at the right of thi valve casing in the same figure; The restriction to flow which the fuel encounters in passing through thevalve unit 34 is a function of the degree to which theannular valve element 46 covers the rectangular fuel port 50 in one side of the valve insert sleeve 44. The

opposite side ofthe insert sleeve has a relatively large aperture 52 which presents a relatively slight restriction to flow. The pistonlike valve element 46 is slidably received inside sleeve44 and is mounted on control rod 30 to move lengthwise of the control rod and thereby vary the restriction to flow of fuel through the valve P011250."

In accordance with the operation of the bellows-and? spring-actuated valve 46, if the valve moves upwardly as it does when pitot-pressure increases, it uncoverstheaperture 50'by a corresponding amount and the rate of flow of the fuel through the valve housing is correspondingly increased. A reduction in pitot pressure permits the spring 28 to stretch the bellows accordingly and move the valve 46 downward by a corresponding amount further to restrict the flow of fuel through the valve housing, hence to the-engine; bellows and spring actuating desired normal rate of flow nut 40 toadjust the-spring loading. The mechanism the valve, establishing the The initial or zero setting of the-opposed of fuel, is set by turningthe thereafter responds automatically to pitot pressure to increase and decrease the flow of fuel as such pressure-- varies and thereby to maintain an approximately constant fuel-air mixture ratio throughout the above-defined supersonic speed range.

Since the flow of the fuel through metering aperture 50 to the engine burners is also directly dependent on fuel pressure drop across valve 34, and since this pressure drop may tend to change with difference in pump speed, variation in burner operation, etc., the rate of flow of fuel through such aperture would vary in some mannen for anysgiven position of valve element 46,..the flow through aperture 50 will always be the same.

Fuel leaving the valve 34 passes into a chamber 56 within the second valve housing 54 and out through.

a port 58. The opening of this port is increased or decreased by axial movement of a conventional tulip. valve 60. The end of the valve body remote from the valve head is cylindrical and is slidably received within the.-:,

A spring 64 urges the valve in the guide sleeve 62. direction to open the port 58 by an amount established by limiting contact of the valve with .a variably posi-" tioned-vvalve-controlling stop comprising the stud 66 aligned with. the :valve as shown.

Thenposition -of .the stud 66,.hence the position of the; valve- 60,.is determined at any time by the fuel. pressure differential between opposite sides. of a diaphragm 68 connected to one end ofthe stud and divid-- ing the pressure chamber 70 into spaces 72 and74. To the space 72 a tube 76 communicates thefuel pressure at the inlet side of the control valve casing 34, while to the other space 74 a tube 78 communicates the fuel pressure in the line at the outlet side of the control valvecasing.

As the differential between the pressures in the tubes 276 and 78 increases, the diaphram, hence the stud 66;" moves in the valve-closing direction by a corresponding amount against the force of spring 64 acting through thebody of the valve 60. This shift of the valve 60-increases the restriction of the valve port'58 and tends to build up sideof such valve. Likewise a tendency for a reduction in such pressure differential by a decrease in fuel pres-' sure on the inflow side of valve 46 or by an increase in fuel pressure the discharge side of such valve, 1esults in opening movement of valve 60 to decrease the restriction of valve port 58, and thereby prevents an appreciable drop in rate of flowof fuel to the engine caused by a tendency for pressure differential to decrease. This regu-' latory action of valve 60 enables the establishment of a flow rate which is related almost directly to the pitot pressure-in the speed'range of interest.

The stationary end of the spring 64 seats against a nut 80 threaded on a thrust-reaction screw 82 which. carries a fixed thrust collar 84 rotatable in the aperture 85 in the end wall of the valve casing 54. The nut 80 has a side extension or tab 86 which is apertured to slide up and down on a vertical guide pin 88, pre= venting rotation of the nut 80 as the screw 82 is turned: Such rotation of the screw causes the nut to travel up,

or down, depending on the direction of rotation. A hexagonal tool socket 90 in the lower endof the screw provides a means for rotating the same, while a lock nut 92 seated against a washer 94 can be tightened to hold the screw in any selected position. This screwand-nut assembly enables establishing the correct initial leading of the spring 64 to give the proper initial relationship, for a given fuel system pressure, between fluid pressure difierential in tubes 76 and 78 and quantity of fuel flow.

It should be borne in mind that the detailed mechanism illustrated for carrying out the principles of the invention, and more especially the details of the control valve assembly including the evacuated bellows and the spring 28, as well as the details of the differential pressure control apparatus associated with valve 60, are not in themselves limiting features, in that other types of mechanism for regulating fuel delivery rate in accordance with pitot pressure may be employed. It will be understood, further, that the illustrated details of the pitot tube may also be varied while producing a similar result. The mouth of the pitot tube should, however, be located away from the shock wave of the engine, and preferably ahead of the leading end of island 14.

I claim as my invention:

In a supersonic aircraft propelled by a ram jet engine, the combination comprising the ram jet engine having a diffuser on the forward end thereof through which air passes in entering the engine, and an island member mounted generally centrally within said diffuser to project forwardly therefrom, said engine being operable to propel said aircraft at varying speeds throughout a predetermined supersonic speed range defined between a lower supersonic speed at which the major shock wave created by and ahead of the engine assumes a substantially conical form and shifts rearwardly to hug the forward end of the island and an upper supersonic speed at which the cone angle of such rearwardly shifted shock 5 pages 36-38.

wave has decreased to a point of interference from said diffuser, means for delivering fuel to said engine including regulator means controllable by air pressure to vary the fuel delivery rate substantially in proportion to air pressure applied to said regulator means, and a source of air pressure for control application to said regulator means comprising a pitot tube mounted in forwardly projecting position on the forward end of the island member with the mouth of the pitot tube directed forwardly into the free air stream at a relative location outside any shock waves from the aircraft operating in said predetermined supersonic speed range, and means operatively applying the air pressure developed within said pitot tube to said regulator means for controlling the same thereby independently of static air pressure, whereby an approximately constant ratio of fuel and mass airflow into said engine is maintained throughout said supersonic speed range.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,858 Knisley Dec. 14, 1937 2,400,701 Meredith May 21, 1946 2,411,484 Watter Nov. 19, 1946 2,422,808 Stokes June 24, 1947 2,441,948 Atkinson May 25, 1948 2,512,790 Cleveland June 27, 1950 2,540,594 Price Feb. 6, 1951 2,545,703 Orr Mar. 20, 1951 2,557,526 Bobier June 19, 1951 2,566,319 Deacon Sept. 4, 1951 OTHER REFERENCES Flight Magazine, Transonic Research, July 11, 1946, 

